The present invention relates to a method and apparatus for compressing gaseous fuel in the rotatable impeller of a gas turbine engine.
A typical gas turbine engine includes a power section, a gear box, and various accessories such as a starter, fuel control, etc. The power section includes a compressor, a turbine, and a combustor. The compressor and turbine sections of the engine can rotate at speeds as high as 100,000 rpms. Air is compressed in the compressor to several atmospheres, for example, before it goes to the combustor. The combustor is split into two zones. At full load, the primary combustion chamber operates at fairly close to stoichiometric, the ideal fuel/air ratio. All of the fuel, and approximately xc2xc of the air or less, start to bum in this zone. The remainder of the air enters the secondary combustion zone through holes in the burner liner. This air provides a relatively cool blanket between the burning gases and the liner before it mixes. This serves to keep the liner cool. It also dilutes the temperature of the hot gases down to the point where the turbine nozzles and wheels will have a long life.
Accordingly, in the combustor, the fuel is burned, which heats the air, which then expands through the turbine wheels. The turbine wheels drive the compressors and, through the reduction gear box, the generator.
It is sometimes desirable to use natural gas rather than diesel fuel in a gas turbine engine because natural gas is generally less expensive, requires no storage tank, burns cleaner, produces significantly less NOx and provides higher efficiency and more power than diesel fuel.
A major problem with the use of natural gas is that it must be compressed enough to enter the combustor, and known gas compressors are very expensive and require significant energy to run. Most of the compressors available are screw-type or reciprocating compressors. They are generally equipped with gas coolers, oil separators, and accumulators.
Due to the high cost of add-on gas compressors, it is desirable to provide a method and apparatus for compressing the gas in a manner which eliminates the add-on gas compressor, while maintaining the required concentration of natural gas in the mixture which is injected into the primary zone of the combustor.
The present invention overcomes the above-referenced shortcomings of prior art gas compressors by providing a gas compressor which is integral with the gas turbine engine. The gaseous fuel is injected into the rotatable impeller (i.e., the compressor) of the engine, and is ejected from the impeller into a selected one of a plurality of diffuser channels positioned peripherally about the impeller. The gas is then directed from the selected diffuser channel(s) to the primary zone of the combustor. The source of gaseous fuel is movable in order to adjust the position at which the gaseous fuel is injected into the impeller so that the fuel is always directed into the selected diffuser channel(s).
More specifically, the present invention provides a gas turbine engine including a rotatable impeller having a plurality of vanes with inlet and outlet ends. A plurality of diffuser channels are spaced apart radially beyond the outlet ends. A movable source of gaseous fuel is positioned adjacent the inlet ends of the vanes for injecting gas into the impeller at a position from which the impeller ejects an air/gas mixture from the outlet ends into a selected one of a plurality of diffuser channels. The movable source of gaseous fuel is movable as a function of the rotational speed of the impeller, whereby the flow of gaseous fuel injected from the movable source is always directed into the selected diffuser channel to facilitate combustion. The fuel from the selected diffuser channel is directed to the primary zone of the combustor so that the appropriate concentration of fuel is maintained for burning in the combustor.
This invention is useful for a variety of gaseous fuels, including natural gas, vaporized propane, vaporized butane, etc.
A further aspect of the invention provides a method of compressing gaseous fuel in a gas turbine engine comprising: a) rotating an impeller about an impeller axis of the gas turbine engine, wherein the impeller includes inlet and outlet portions at opposing ends of a plurality of vanes; b) injecting gaseous fuel from a movable source of gaseous fuel into the inlet portions such that the fuel travels along the vanes and through the respective outlet portions to a selected one of a plurality of diffuser channels spaced apart radially beyond the outlet portions; and c) adjusting the position of the movable source with respect to the impeller axis based upon the rotational speed of the impeller to ensure that the injected gaseous fuel enters the selected one of the diffuser channels as the rotational speed of the impeller is varied. The gaseous fuel is then directed from the selected diffuser channel to the primary zone of the combustor for burning.
The adjustment of the movable source may be accomplished by capturing pressurized air exhausted from the impeller and using the compressed air to move a piston connected to the movable source, or electrically by a servomotor.
Accordingly, an object of the present invention is to provide a method and apparatus for compressing gaseous fuel for use in a gas turbine engine in a manner in which the add-on gas compressor is eliminated.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.